RFC2616 defines #rules as:

   #rule
      A construct "#" is defined, similar to "*", for defining lists of
      elements. The full form is "<n>#<m>element" indicating at least
      <n> and at most <m> elements, each separated by one or more commas
      (",") and OPTIONAL linear white space (LWS). This makes the usual
      form of lists very easy; a rule such as
         ( *LWS element *( *LWS "," *LWS element ))
      can be shown as
         1#element

It also defines Linear White Space (LWS) as:
   LWS            = [CRLF] 1*( SP | HT )


The actual implementation only accepts SP (Space) and not HT (Horizontal Tab) when parsing cache related header fields (i.e. "Vary", "Cache-Control" and "Pragma")

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1710723 13f79535-47bb-0310-9956-ffa450edef68